A combing sound is generated when a comb or brush is run through a person's hair. This sound is generally louder in the case where the surface of the hair is significantly damaged. This is because the friction between the teeth of the comb or brush and the hair is greater than the case where hair is undamaged. By contrast, the combing sound is softer where a person's hair is less damaged or the surface of the hair is smoothened by a hair care product.
Given the above relationship, various systems for estimating hair characteristics such as hair damage or a change of hair condition attributable to a hair care product based on the combing sound are proposed. For example, (the publication in J. SOC. COSMETIC CHEMISTS, Vol 17, pages 171-179 (1966)) describes a device which includes a comb or brush provided with a microphone fixed at a central point of the back of the comb or brush, and a signal amplifier for amplifying a combing sound signal detected by the microphone when the comb or brush is run through a person's hair, (Published Japanese Translation No. 2004-527730 of PCT International Application) describes a device which is based on the same principle as Japanese Patent Application Laid-open No. 2004-159830 which describes a device which performs a frequency analysis of a combing sound signal by performing Fourier transform and is arranged to output the amplified combing sound signal from a speaker as an audio output.
In the above case, where the comb or brush is provided with a microphone centrally fixed at a central portion of the back of the comb or brush, when run through hair, the combing sound contains a large amount of noise from many external sources. Therefore, even if the combing sound signal detected by the microphone is amplified and converted to an audio output, it remains difficult to distinguish the combing sound from other noise sources. Therefore, estimation of the hair characteristics such as hair damage based on the combing sound output as the audio output is difficult via existing sensors.